Telescoping valves are used to control the level of fluid, for example in a storage or water treatment tank or the like. The valve comprises a vertical slide pipe (1) (also called a "slip tube"), the upper end (5) of which serves as a weir, and the lower end (6) of which extends through a hole (16) in the bottom of the tank (18) into a conduit of some kind. The slide pipe (1) can vary from several inches to several feet in diameter, and may be many feet high, depending on the application. When the water level is higher than the upper end (5) of the pipe, the water overflows into the pipe (1), and the level in the tank is maintained at the level of the weir (5). Commonly, the weir (5) is provided with V-shaped notches (4), permitting the water to begin flowing at an increasing rate as it approaches the top of the weir.
The slide pipe (1) can be raised or lowered by an actuating mechanism (which does not form part of the invention, and is not shown) which is attached to the top of the slide pipe (1), for example by a U-shaped bracket (3) which is attached to an actuating rod (2) or pipe. Actuation of the actuating mechanism raises and lowers the actuating rod (2), which in turn sets the height of the top (5) of the slide pipe (1) above the bottom (18) of the tank, and thus determines the water level in the tank.
Prior art telescoping valves are prone to leakage around the hole (16) where the slide pipe (1) passes into a pipe of larger diameter with a tank flange at the bottom (18) of the tank. Such leakage is expected, and it is not uncommon for a specification for a telescoping valve to contain a value for permissible leakage which is quite substantial. Often a large flat neoprene or rubber washer or gasket is used around the slide pipe as a wiper. The washer is typically held to the tank flange with a flat metal flange, which compresses the rubber to some extent. Such a wipe gasket can achieve a poor seal, at best, and both the slip tube and actuating mechanism must be removed from the drained tank to replace the gasket if such replacement is needed.
Mechanical Joint ("MJ") gaskets are normally used as a watertight packing in mechanical joint cast iron fittings, in installations where it is not possible to know the exact laying lengths of the pipe in advance. One end of a piece of pipe is inserted into a larger diameter section of pipe known as an "adjustable connecting piece". The MJ gasket is then squeezed into the gap between a tapered portion of the inner wall of the connecting piece and the outside wall of the pipe by a ring gland, forming a seal primarily on its inside straight walls. This application is completely different from the resilient valve seat in the present invention, the MJ gasket being used here purely for commercial ease of availability and economic reasons.
The present inventor has previously used an MJ gasket in a valve, as shown in U.S. Pat. No. 5,280,875 "RESILIENT SEAT MUD VALVE". Mud valves, however, are a different type of application than telescoping valves, in that the seal is used there to seal between a plug and a hole, as opposed to providing a replaceable leak-free sliding joint between a sliding pipe and a flange.